It happens with either 4.4 and 4.5 and I used the 'Groove 02' animation from Actorcore in the test
I think I know what it is.
If I export an animation from CC4.5 its fine, but I have been downloading packs from Actorcore because I can get them as one FBX pack instead of having to export them from CC4 individually.
As you can see the example from the Clumsy move pack, from CC4 its fine, but from the Actorcore site, it screws up. It does it all packs 10 packs I've bought from Reallusion
They work fine on 1.35 but on 1.36 the actorcore downloads all screw up when exporting for Unreal.
It also seems to do it on any fbx animation that doesn't come from CC441% of original size (was 1224x614) - Click to enlarge